I would recommend avoiding creatures like bears and trolls until you're a higher level if you've tried fighting them. Bandits should be fairly easy if you time your blocks and bashes well, strafe or jump right before an archer fires (After the bow is fully drawn), and use poisons like paralysis on the bosses. Also, having a strong follower like Lydia will help a bit.Edit: Also, if you're heavily melee-based, invest greatly in Smithing to improve gear quality.

Get a dog (like Meeker), use your housecarl. They may delay leveling up, and are not terribly stealthy but can save you a lot of hits when you are "young". Two handed swings are slow so it's helpfull to have somebody distracting your opponents. Major Moolahs potions advice is good too.

Level up your alchemy. Strong melee isn't going to cut it, so you'll need poisons and potions with multiple buffs. Other than that, stick and move. Strafe around their back. You won't last long going toe to toe with everybody.

thats all great general advice, but the truth of the matter is that all ES games have worked the same way. they punish you for not choosing a specialty. I don't mean that you have to pick between melee stealth and spells, but you do have to pick two or three skills from amongst those available and use them primarily. grabbing any random skill that seems interesting might be fun for a while but the issue you run into (and that you've already run into) is that you level up too fast. if you pick just a few skills then by the time you hit 15 they may be in the 65-75 range, whereas if you don't specialize then they'll all stay in the low 40s. YOU MUST CHOOSE.

Now then, to solve your current problem without starting over its going to take a bit of time. step one (as above) is to choose a specialty. once that's done take what money you can spare and spend it on levelling up one of those (preferably a combat based skill) at a trainer. do that every time you level for a little while. next, do what it takes to get yourself some new equipment. you should probably have dropped that steel for something better around 11-12. weapons are the most cost effective though so if it comes down to a new weapon or new armor grab the weapon. Go ahead and enchant that weapon with whatever minor enchantment you can manage and try to keep it charged. Finally, grab a follower and a dog if possible and head out. for the time being your goal is not to level so dont mind the fact that they're stealing your experience. what you want is the loot. the shiny shiny loot. this is where you should get your armor.

in terms of what quests you should be taking on i would suggest you play through some of the first civil war quests as the first of those involve you and a large group raiding tombs where you might find some new items without much hassel.

Though you haven't been focusing on anything specific to level up, it's not to late to start. Leveling up specific skills is what makes each character unique and powerful and specific things. If you are using two handed and heavy armor, start putting perk points into these and look at other skills you maybe interested in also.

I would like to add to all the other already excellent advice offered above is to not ignore STRATEGY. There are many ways to skin a troll or a sabre cat. If there is a trap nearby, use it. If there is another enemy nearby, lead the whatever is kicking your butt to it. In my very first game, I antagonized a dragon into following me to a powerful mage and he killed that pesky magician for me. Then his health was low enough for me to deal with him.

Recently when starting a new game I took on a quest a bit too early and found that the enemies were much too powerful for me. I crouched above them in one room and took them out one by one by shooting an arrow down on the floor to start them looking for me, which caused them to move into range where I could take potshots with my bow until they were all dead. It required great patience, but I have lots of patience.

I once killed two Mammoths by leading them to where there were some pillars I could get between. The Mammoths could not get in between the pillars and I was eventually able to take them down with poisoned arrows.

Do not let yourself be surrounded and do not allow a powerful enemy to close with you. An Orc can do incredible damage to you and usually wields a greatsword. Back off and zap him with fire or arrows. Try to take on multiple enemies in a narrow corridor so that they can only reach you one at a time.

Shoot those hanging lamps into the oil!

Also do not be ashamed to retreat or to go around. On my way up a high mountain in a recent game, at about level 15, a Troll sent me to Sovngard several times. Finally I ran up the side of the mountain into some trees and played hide and seek with him for a bit, then worked my way around him and ran as if all the demons in Oblivion were on my tail, up the trail to my goal. Once I got out of his range he quit following.

As Farengar will tell you if you listen to him, your brain is your best weapon. Use it.

I don't know why anyone needs or suggests followers. They're annoying, get in the way and the damage they do could be you getting hit for armor perk, or you landing blows with spells/weapon. I guess they're ok at a higher level when lvling is a non issue.

Follower ARE annoying and they can be a definite liability in a battle. If you are concentrating on strategy, you do not need a follower barging in or setting off traps. I use followers only in specific situations and then only those I know will be able to provide the help I need.

also, a note on strategy: some character builds rely on certain strategies and some strategies are simply more effective than others. as an example, a one almost infallible build is to level sneaking, conjuration, and illusion. The idea is to prevent yourself from ever having to fight more than one enemy at a time. on seeing a group of enemies you use illusion to frenzy one and let them fight it out while you remain hidden. once one is dead you raise it as a zombie to continue the fight or if there are more than two you can frenzy another. If you come across a single opponent and cant rely on his friends to kill him you can still conjure up an ally and outnumber him.

keep such strategies in mind when building a character. Swinging a sword is fun and basic but its not always the best choice.

also, a note on strategy: some character builds rely on certain strategies and some strategies are simply more effective than others. as an example, a one almost infallible build is to level sneaking, conjuration, and illusion. The idea is to prevent yourself from ever having to fight more than one enemy at a time. on seeing a group of enemies you use illusion to frenzy one and let them fight it out while you remain hidden. once one is dead you raise it as a zombie to continue the fight or if there are more than two you can frenzy another. If you come across a single opponent and cant rely on his friends to kill him you can still conjure up an ally and outnumber him.

keep such strategies in mind when building a character. Swinging a sword is fun and basic but its not always the best choice.

An excellent suggestion. I have never focused on magic use so I didn't think of it. I like a ranger/stealth character and use the bow almost exclusively. I shall have to work on that. I have yet to start the College quest in this game and my magic use is nil. I need to try it.